The present invention relates to mechanically strengthened nonwovens for the production of dimensionally stable, flexible molded articles.
The term "mechanically strengthened nonwovens" is understood to imply nonwovens which are mechanically strengthened by means of barbed needles in needle-punching, by water jets according to the spunlaced procedure, or by coulier needles in a stitchknitting method. These nonwovens may be manufactured, for example, by using polyester fibers stretched or partially stretched as polyethylene terephthalate fibers, as bicomponent fibers of polyethylene terephthalate polymers having differing softening points, or as homopolymeric melded fibers.
There are several techniques to manufacture nonwovens for moldings. For example, according to the so-called thermofusion procedure, these nonwovens of coarse polyester fibers (PES) having a portion of PES-bicomponent fibers (core/sheath) are deformed under pressure and temperature after solidification. The enveloping layer of the bicomponent fibers starts to fuse, thus causing the polyester fibers and the bicomponent fibers to fuse together at their crossings. This method is described in the journal "Techtextil Telegramm", 1991, number 21, page 3. The production of PES-spunbonded nonwovens using special binding fiber components represents another technique; under pressure and temperature these are processed into molded parts having a deformation depth of 35 cm, for example, used as primary substrate for formed tufted carpets (Konferenz Einzelbericht: Textilien im Automobil, Kongre.beta. der VDl-Gesell. Textil und Bekleidung, 1993, Dusseldorf, Oct. 14th-15th 1993, pages 9-23).
Furthermore, mechanically strengthened nonwoven mats are known which, composed of three plies (covering nonwoven-filling nonwoven-covering nonwoven), are deformed under heat and used as supporting substrate for molded articles. This method is described in Konferenz Einzelbericht: 32nd Int. Chemiefasertagung 1993, Dornbirn, Austria, Sept. 22nd to 24th 1993, pages 1-25, Paper No. 68.
The known techniques permit the production of molded articles made of pure-grade fibrous materials which may be recycled.
Although extensive deformations may be achieved, these methods have the disadvantage that, in case of an extreme deflection angle and sophisticated forms, the materials break at the points of deflection or form weak points. To obtain a dimensionally stable deformation, these nonwovens must be strengthened to a high degree, and this results in loss of flexibility.